Field of the Invention
The aspects of the present invention relate to an element substrate for a liquid ejecting head and a wafer including a plurality of element substrates, and particularly to a configuration that prevents electro-static discharge (ESD) damage (hereinafter, may be referred to as ESD damage) to the element substrate.
Description of the Related Art
A liquid ejecting apparatus such as an inkjet printer is known as an example of information output apparatuses configured to record information such as a character and an image on a recording medium such as a sheet and film. The liquid ejecting apparatus includes a liquid ejecting head that applies liquid droplets onto a recoding medium for recording. A thermal inkjet process is known as an example of liquid ejecting processes performed by the liquid ejecting head. In the thermal inkjet process, a current is passed through the heating resistor, which is in contact with the ink, for about a few μ seconds to generate a thermal energy. The bubbling of the ink caused by the thermal energy is used to eject the ink droplets. The liquid ejecting head for the thermal inkjet process generally includes an element substrate including a heating resistor used for ejection of the ink droplets. The element substrate includes a silicon substrate, an element forming member including the heating resistor, on the silicon substrate, and a discharge port forming member including a discharge port, on the element forming member.
In a production step of the element substrate or in a recording operation by the liquid ejecting head, the element substrate may have ESD damage. Japanese Patent Laid-Open No. 2004-050636 describes that a dummy MOS (Metal-Oxide-Semiconductor) is connected in parallel with the heating resistor so as to prevent the ESD damage to the heating resistor (heater). A current flowing from the pad flows to the dummy MOS, preventing a large current from flowing into the heating resistor.
U.S. Pat. No. 7,267,430 describes that an anticavitation layer is connected to a grounded-gate MOS. The ESD current flowed into the anticavitation layer flows to the substrate through the grounded-gate MOS. Thus, the protective film between the anticavitation layer and the electrode for the heating resistor is unlikely to have the ESD damage.